1. Field of the Invention
This invention relates to the field of radio frequency identification (RFID) devices, and a method of manufacturing such devices.
2. Description of the Related Art
RFID tags and labels have a combination of antennas and analog and/or digital electronics, which may include for example communications electronics, data memory, and control logic. RFID tags and labels are widely used to associate an object with an identification code. For example, RFID tags are used in conjunction with security-locks in cars, for access control to buildings, and for tracking inventory and parcels. Some examples of RFID tags and labels appear in U.S. Pat. Nos. 6,107,920, 6,206,292, and 6,262,692.
RFID tags and labels include active tags, which include a power source, and passive tags and labels, which do not. In the case of passive tags, in order to retrieve the information from the chip, a “base station” or “reader” sends an excitation signal to the RFID tag or label. The excitation signal energizes the tag or label, and the RFID circuitry transmits the stored information back to the reader. The “reader” receives and decodes the information from the RFID tag. In general, RFID tags can retain and transmit enough information to uniquely identify individuals, packages, inventory and the like. RFID tags and labels also can be characterized as those to which information is written only once (although the information may be read repeatedly), and those to which information may be written during use. For example, RFID tags may store environmental data (that may be detected by an associated sensor), logistical histories, state data, etc.
Methods for manufacturing RFID labels are disclosed in PCT Publication No. WO 01/61646 by Moore North America, Inc. The method disclosed in PCT Publication No. WO 01/61646 uses a number of different sources of RFID inlets, each inlet including an antenna and a chip. A plurality of webs are matched together and RFID labels are die cut from the webs, to produce RFID labels with liners. Alternatively, linerless, RFID labels are produced from a composite web with a release material on one face and pressure sensitive adhesive on the other, the labels formed by perforations in the web. Various alternatives are possible.
Still other RFID devices and methods for manufacturing RFID labels are disclosed in U.S. Patent Application Publication No. US2001/0053675 by Plettner. The devices include a transponder comprising a chip having contact pads and at least two coupling elements, which are conductively connected with the contact pads. The coupling elements are touch-free relative to each other and formed in a self-supported as well as a free-standing way and are essentially extended parallel to the chip plane. The total mounting height of the transponder corresponds essentially to the mounting height of the chip. The size and geometry of the coupling elements are adapted for acting as a dipole antenna or in conjunction with an evaluation unit as a plate capacitor. Typically, the transponders are produced at the wafer level. The coupling elements can be contacted with the contact pads of the chip directly at the wafer level, i.e., before the chips are extracted from the grouping given by the wafer.
In many applications, it is desirable to reduce the size of the electronics as small as possible. In order to interconnect very small chips with antennas in RFID inlets, it is known to use a structure variously called “straps”, “interposers”, and “carriers” to facilitate inlay manufacture. Interposers include conductive leads or pads that are electrically coupled to the contact pads of the chips for coupling to the antennas. These pads provide a larger effective electrical contact area than ICs precisely aligned for direct placement without an interposer. The larger area reduces the accuracy required for placement of ICs during manufacture while still providing effective electrical connection. IC placement and mounting are serious limitations for high-speed manufacture. The prior art discloses a variety of RFID strap or interposer structures, typically using a flexible substrate that carries the interposer's contact pads or leads.
One type of prior art RFID inlet manufacture using interposers is disclosed in European Patent Application EP 1039543 A2 to Morgan Adhesives Company (“Morgan”). This patent application discloses a method of mounting an integrated circuit chip (IC) using an interposer connected across a gap between two thin conductive film sections of a conductive film antenna. The interposer comprises a thin substrate having two printed conductive ink pads. This method is said to be suitable for mass production of radio frequency identification tags (RFIDs) by mounting ICs on interposers that are then physically and electrically connected to the antenna sections using a pressure sensitive conductive adhesive. The pressure sensitive conductive adhesive provides a direct electrical connection between the interposer contact pads and the antenna sections.
Another type of prior art RFID inlet manufacture using interposers is based on a technique for manufacturing microelectronic elements as small electronic blocks, associated with Alien Technology Corporation (“Alien”) of Morgan Hill Calif. Alien has developed techniques to manufacture small electronic blocks, which it calls “NanoBlocks”, and then deposit the small electronic blocks into recesses on an underlying substrate. To receive the small electronic blocks, a planar substrate is embossed with numerous receptor wells 210. The receptor wells are typically formed in a pattern on the substrate. For instance, the receptor wells 210 may form a simple matrix pattern that may extend over only a predefined portion of the substrate, or may extend across substantially the entire width and length of the substrate, as desired. Alien has a number of patents on its technique, including U.S. Pat. Nos. 5,783,856; 5,824,186; 5,904,545; 5,545,291; 6,274,508; and 6,281,038. Further information can be found in Alien's Patent Cooperation Treaty publications, including WO 00/49421; WO 00/49658; WO 00/55915; WO 00/55916; WO 00/46854 and WO 01/33621.
As noted above, RFID inlets using interposers provide an inherent advantage in high speed manufacture by facilitating effective mechanical and electrical connection of ICs to antennas. However, other substantial manufacturing problems must be solved in order to provide an efficient inlay production process using interposers. U.S. Published Patent Application No. 2003/0136503 A1, commonly assigned herewith, discloses processes for producing RFID interposers and attaching the interposers to an antenna web. The interposers are severed or separated from a webstock or sheetstock with densely packed IC's (i.e. small pitch between adjacent ICs) and interposer leads. The interposers are then transported, “indexed” (spread apart), and affixed in sequence to a webstock containing antennas that are typically spaced at a much higher pitch.
Other patent publications disclosing systems for attaching interposers to antennas to form RFID transponders include for example: U.S. Patent Application 2004/0089408 A1 (connecting micro-chip modules to antennas via release from a carrier tape, then crimping or soldering to the antennas); Japanese Patent Application No. JP 2003 281491 A (mounting the interposer to circuits using an electronically controlled, rotating transport members); and PCT publication WO 2005/076206 A1 (continuous production of electronic film components by placing chip modules on antenna connections of antenna film sections).
Increases in demand for RFID labels and tags have necessitated substantial increases in production capacity. It will be appreciated that higher production rates and lower costs for RFID devices would be desirable.